I. Field of the Invention
This invention relates generally to the mechanical design of a header for an implantable medical device, such as a cardiac pacemaker or cardiac pacemaker/defibrillator, and more particularly to the design of a header having a lead receiving bore with contacts for mating with either a unipolar lead or a bipolar lead.
II. Discussion of the Prior Art
An implantable medical device typically comprises a metal housing hermetically sealing a battery, a pulse generator circuit and a microprocessor-based controller for the pulse generator such that cardiac stimulating pulses are generated on a timed basis determined by the microprocessor-based controller. Affixed to an exterior wall of the housing is a header for operatively coupling the contacts on the proximal terminals of one or more medical leads to feed-through pins that enter the housing through seals where they connect to circuit inputs and outputs.
The medical leads involved may be unipolar or bipolar. A unipolar lead comprises an elongated flexible, plastic lead body having a conductor running the length thereof for connecting an electrode at a distal end thereof to a contact on a terminal on the proximal end thereof. A bipolar lead will have a distal tip electrode and a ring electrode on the surface of the lead body located proximally of, but close to, the tip electrode. Conductors again run the length of the lead, connecting the tip and ring electrodes individually to a conductive pin and a ring contact on the bipolar lead's proximal terminal.
In the past, manufacturers of implantable medical devices generally offer a plurality of models, each with differing functionality and operating modes. Each such model might be compatible with either a unipolar lead or a bipolar lead, but not both. Thus, if a patient happen to have a unipolar lead implanted, it would be necessary to select a stimulating device having a header that would accept a unipolar lead. If, on the other hand, the patient had a bipolar lead implanted, a model having a header with contacts for mating with the proximal terminal of a bipolar lead would have to be selected.
It should be obvious, then, that if the device manufacturer offered, say, six models of a cardiac stimulating device exhibiting different functionality, it would be necessary to stock 12 different models to assure that each of the six could operate with either unipolar or bipolar leads. This necessarily increases the cost of inventory, and when it is considered that such devices have a limited shelf life, it will frequently happen that units will have to be scraped because of a lack of demand for particular models.
It will be seen, then, that a considerable savings can be realized if a header were designed that could accept either a unipolar lead or a bipolar lead. Unique headers would not have to be made to accommodate the two types of proximal lead terminals in that one such header would work with each type of lead.
It is accordingly a principal object of the present invention to provide a header for an implantable medical device that can accept the proximal lead terminal of either a unipolar or a bipolar lead in a single proximal lead terminal receiving bore.